Crystal plate and method of fabricating same



G. J. BOKENY July 6, 1948.

CRYSTAL PLATE AND METHOD OIF FABRICATING SAME 2 Sheets-Sheet 1 FiledSept. 7, 1944 CF- H C" INVENToR 652A J. BOKENY ATTaRNEY July 6, 1948- G.J. BOKENY 2,444,590

CRYSTAL PLATE AND METHOD OF FABRICATING SAME 2 Sheets-Sheet 2 File'dSept. 7, 1944 INVENTOR. Gaz/a J. BoxzNY NEY Patented July 6, 1948CRYSTAL PLATE AND METHOD OF FABRICATING SAME Geza J. Bokeny,

Cleveland, Ohio, assignor to The Brush Development Company, Cleveland,Ohio,

a corporation of Ohio Application September 7, 1944, Serial No. 553,096

15 Claims. 1

This invention pertains to a fabricated piezoelectric crystal elementand a method of fabricating it.

More particularly this application relates to the fabrication ofexpander plates and multiplate flexing elements of P-type piezoelectriccrystalline material.

An object of my invention is to provide an expander piezoelectric plateof an unusually large size.

Another object of my invention is to provide a method of fabricatinglarge expander plates of P-type piezoelectric crystalline material.

Another object of my invention is to eiciently use substantially'all ofthe clear unflawed crystalline material in a P-type crystal bar formaking expander plates.

Still another object of my invention is to so cut and reassemble one ormore crystal shear bars or shear plates of P-type crystalline materialthat expander bars or expander plates oi maximum size are obtained.

Other objects and a fuller understanding of my invention may be had byreferring to the following description and drawings in which:

Figure 1 is an isometric view of a P-type crystal bar.

Figure 2 is a plan view of a shear plate and showing the relationship ofan expander plate to a shear plate.

Figures 3 and 4 are end views of severed crystal bars or plates lookingin a direction parallel to the Z-axis of the crystalline material.

Figures 5 and 6 illustrate expander bars or plates fabricated byreassembling the portions of the bars or plates shown in Figures 3 and4.

Figure '7 illustrates still another method of assembling cut portions ofa shear bar or shear plate to form a large expander bar or plate.

Figure 8 illustrates another method of cutting a shear bar or plate.

Figure 9 illustrates how the portions cut from the bar or plate inFigure 8 may be reassembled to form an expander bar or an expanderplate.

Figure 10 illustrates still another method of cutting a shear bar orshear plate.

Figures 11 and 12 illustrate by plan and side views a multi-plate exingelement comprised of two or more built up expander plates such as thevplate shown in Figure 9.

Figures 13 and 14 illustrate still another form of my invention.

Figures 15 and 16 illustrate another form of my invention.

In the production of expander plates and of multiplate exing elements itis often desirable to obtain plates having large areas which cannotreadily be cut from crystal bars of the size which are easily grown atpresent.

In the process of growing crystals, a large number of crystal bars willhave an average cross-sectional area; a small percentage of the barswill have smaller cross-sectional area and a small percentage will havea cross-sectional area somewhat larger than the average. 'In order toobtain large expander plates and large multi-iplate flexing elements ithas been necessary to cut plates from the select few crystal bars whichhave the largest cross-sectional area, and often these bars are notlarge enough to yield the required large plates.

In Figure 1 there is illustrated a crystal bar i5 which has been grownfrom a seed crystal I6; the seed crystalfhaving been grown from a seedplate I1. This crystal bar I5 illustrates a P-type crystal. This type isto be understood as comprising primary ammonium phosphate (NHrHzPOl)primary potassium phosphate, primary rubidium phosphate, the primaryarsenates of ammonium, potassium and rubidium, isomorphous mixtures ofany of these named compounds and all other piezoelectrically activecrystalline material isomorphous therewith.

In Wyckoffs Structures of Crystals (2nd edition, N. Y. 1931) thiscrystal type is introduced as the iii-121304I type. In theStrukturbercht (Supplement to Zietschrit fuer Kristallography) this typeis designated as type H-2-2.

The habit of this P-type crystal is a combination of the secondary prismand the secondary ley-pyramid. (See Figure 2.) It is characteristic forthe P-type crystals that they are elongated parallel to the axis of theprism, which is the optic axis of these crystals and designated asZ-axis in this patent.

All the crystals enumerated above as members of the P-type group -belongto the crystallographic symmetry class designated commonly by the symbolVe. This class is also known as the di-tetragonal alternating crystalclass or as the tetragonal sphenoidal class, the latter name being theone used in Dana-Ford, Textbook of Mineralogy, 4th ed., N. Y., 1932.This crystal class is characterized by the presence of three two-foldaxes of symmetry perpendicular to each other and two planes of symmetryat right angles to each other and intersecting in one of the twofoldaxes. The planes cut the other two two-fold axes under angles of 45.This combination of symmetry elements makes that axis which is parallelto the two planes oi' symmetry a four-fold alternating symmetry axiswhich is also the optic axis of the crystal.

Shear -plates are obtained from the crystal bar II by slicing or cuttingin a plane parallel to the plane indicated by the line Il. These platesmay be oi' any desirable thickness.

Figure 2 illustrates a shear plate I 9 and also illustrates an expanderplate which may -be cut from the shear plate I9. It will be noted thatthe major edges oi' the expander plate 20 lies at angles of 45 to the X,Y axes of the crystalline material, and that the major face areasthereof are substantially 'normal to the Z-axis of the crystallinematerial. In the past in the fabrication of expander plates the cornerpieces of the shear plate I9 have been wasted, and an expander plateobtained from a sheer plate has been considerably smaller in area thanthe shear plate' from which it was obtained.

According to my invention two shear plates or shear bars 2|, 22 areutilized for obtaining a large expander plate or bar whosecross-sectional area is substantially equal to the sum of thecross-sectional areas of the two plates or bars 2|, 22.

I speak of shear plates or shear bars 2|, 22. This is for the reasonthat my invention includes cutting the crystal bar I5 of Figure 1 into anumber of shear plates and then cutting the shear plates andreassembling the sections in accordance with my invention, and it alsoincludes cutting the crystal bar I 5 into two clear substantiallyunilawed shear bar portions, such as by cutting the seed crystal i8 outvoi? the center thereof and thereafter cutting those two shear barportions and reassembling them in accordance with my invention.

I shall describe my invention in connection with assembling plates, butit is to be understood that it is also applicable to assembling bars;substantially the only difference being that the expander bars aresomewhat more easily assembled. Once assembled, however, they must becut perpendicular to the Z-axis to obtain expander plates. This slicingoperation is sometimes apt to disturb the adhesive which holds theportions together. This disadvantage is not met when the plates are rstsliced to their proper thickness and then connected together.

After a pair oi' shear plates 2|, 22 has been obtained each is polarizedto determine its direction of expansion under the influence of a givenelectrostatic iield. These directions of expansion for a given ileld areillustrated by the arrows on the surface of the plates. The plates areground or milled until their edge faces are planar and form a rectangle.The plate 2| is then cut along line 23 which is parallel to thedirection of expansion for the given electrostatic iield therebyestablishing two triangularly shaped crystal portions A and B. Thecrystal plate 22 is cut along line 24 which is substantially normal tothe direction of expansion of the crystal under the iniluence oi' thegiven electrostatic field to establish two triangularly shaped crystalportions C and B. The four triangularly shaped crystal portions A, B, C,and D are then rearranged as is shown by Figure 5 so that the directionof expansion in each crystal portion under the influence of the givenelectrostatic field is parallel to the direction of expansion of theother crystal portions. This is shown by the relationship of the arrowsin Figure 5. The direction of contraction in each of the four crystalportions A.. B, C, D for the given field is perpendicular to thedirection of expansion. vThe triangularly shaped crystal portions A, B,C and D are then connected together by their edge faces. Suitableadhesives such as "Vinylite" or Bakelite cements may be used. By thisprocess there is obtained an expander plate which is twice as large aseither of two shear plates from which it is obtained, and which is i'ourtimes as large as the largest square expander plate that could be cutfrom one of the shear plates.

While in the description of this invention I have illustrated anexpander plate formed from two shear plates, it is to be understood thatany number of shear plates may be cut and the triangularly shapedportions obtained therefrom reassembled to form a large expander plateso long as the proper attention is paid to the directions of expansionoi the several pieces which form the expander plate. The large expanderplate 30 which is shown in Figure 5 may be sold in the form illustrated.or it may have an electrode put on each of its major faces to form anexpander unit which may be used in a variety of devices such asmicrophones, loudspeakers. phonograph pickups and pen recorders, and itmay first be cut to the required shape, and then sold. Particular careshould be exercised if the plate is to be used in a motor device whichconverts electrical energy into vibrational mechanical energy, to assurethat the adhesive utilized for securing the plates together be asuiliciently good insulator that electrical breakdown along theconnection lines does not occur.

I have found that Bakelite adhesive will bond portions of crystaltogether much more firmly than Vinylite cement. However, it is a veryhard, brittle, and unyielding engagement compared to a Vinylite"adhesive Joint. Occasionally when Bakelite" cement has been utilized toconnect the several bar portions together to form an expander bar,subsequent slicing by an abrasive wheel or by a thin saw has set upsufflcient vibration to crack the brittle "Bakelite" cement. TheVinylite" cement, however, has a slight amount of yield or give to it,and when expander bars are made with it they can be sliced into thinplates without splitting along the adhesive lines. Thus, I prefer"Vinylite" cement i'or securing the expander bars. Bakelite" cement,however, is a stronger adhesive so I prefer it for securing expanderplates if no further machining is to be done.

Figure 6 illustrates another way in which the four plates A, B, C, and Dmay be put together to obtain a large expander plate. This method leavesa hole 3| yat the center of the four plates and it is contemplated thatthe hole Il be nlled with an insulating material such as a Bakelite pegor the like or by adhesive material prior to electroding the expanderplate. In this construction it is necessary to either grind or mill awayone corner oi' each oi the triangularly shaped portions in order to forma rectangular plate.

Figure 7 illustrates still another way of positioning the fourtriangularly shaped crystal portions A, B, C, D, when they are cementedtogether. By thus positioning the four portions, the four apexes do notcome together at one point and thus the plate is somewhat strongermechanically than the plate shown in Figure 5.

Figure 8 illustrates a method of cutting a single shear plate into threetriangularly shaped portions, and Figure 9 illustrates how to reasvsurface of the crystal.

46 in a direction perpendicular to its direction semble the threeportions to obtain a rectangular expander plate. The shear plate 40 ofFigure 8 rst is polarized, as has been explained in connection withprevious figures, to determine its direction of expansion for a givenexciting electrical field. This direction is illustrated by the arrowson the plate. The plate is then cut along a first line 4I which isparallel to that direction of expansion to obtain two substantiallysimilar triangularly shaped crystal pieces. Either one of these twopieces is then cut along a line such as `line 42 to'obtain twosubstantially similar triangularly shaped crystal portions F and G.Thus, the shear plate 40 is cut into 3 similar right triangles E, F, andG; F and G being of the same size and substantially half the size of thetriangular portion E. These three crystal portions E, F, and G arerearrangedas is illustrated by Figure 9 so that a rectangular expanderplate is obtained and so that the direction of expansion of eachtriangularly shaped crystal piece for a given exciting electrical fieldis parallel to the direction of expansion of the other two pieces. Thethree pieces are then secured together such as by an adhesive. Thus itwill be seen that the expander plate of Figure 9 has an areasubstantially equal to the area of the shear plate of Figure 8. Ofcourse, the process of sawing or otherwise severing the shear platescauses the loss of some crystalline material but the amount is verysmall especially when compared with the previous process wherein largecorner areas of a shear plate were unusable.

Figure 10 illustrates a shear plate 45 which has been polarized todetermine its direction of expansion. for a given electrostatic field,this direction being illustrated by the arrows on the It may be cutalong line of expansion under the influence of the electrical field toestablish two equal triangularly shaped crystal portions one of which isindicated by the reference letter J and the other of which is cut intotwo smaller triangularly shaped portions H and K. These three crystalportions H, J, and K may be reassembled to establish an expander platehaving the same shape as the plate shown in Figure 9, the onlydifference being that the direction of expansion as indicated by thearrows will be perpendicular to the direction of expansion of the platein Figure 9.

Multi-plate flexing elements may be made from any of these expanderplates, such, for example, as the unit, illustrated in Figures ll. and12. I have found that when a multi-plate flexing element is to be madefrom two or more plates of the type illustrated in Figure 9 it isdesirable to have the connection lines such as the lines 59 and 5i ofone plate lie substantially normal to the connection lines 52 and 53 ofthe other plate. The reason for this is that unless adhesives areutilized which have a greater mechanical strength than the crystallinematerial a weak line will be established in the multi-plate unit if oneconnection line is superposed on the other connection line. Byfabricating composite plates and assembling them into a multi-plate unitwith the fabrication or connection lines at right angles to each otherthis weakness is substantially avoided, and each plate strengthens theother plate.

Figures 13 and 14 illustrate another form of my invention where only oneof two similarly shaped plates 55, 56 is cut along its diagonals, andthe resulting triangularly shaped portions A,

. 6 B, C, D are connected to the uncut plate 56 as shown by Figure 1,4.As has previously been explained, the pclarities of the various platesconnected must be such as to result in the composite plate becoming anexpander plate.

While I have described my invention with a certain degree ofparticularity it is to be understood that modifications in the procedureand to a certain extent in the arrangement of parts may be made withoutdeparting from the spirit and scope of my invention.

I claim as my invention:

1. In the process of fabricating P-type expander plates, the steps of:providing at least two square Z-cut P-type crystal plates, determiningthe direction of expansion for each plate for a given excitingelectrical field, cutting each of said plates diagonally 'in half, andconnecting the four half plates together by their edge faces to form asingle composite rectangular plate with the directions of expansion ofthe four half plates aligned.

2. In the process of fabricating P-type expander plates, the steps ofproviding a pair of similar substantially square Z-cut P-type crystalplates, determining the direction of expansion of each plate for a givenexciting electrical field, cutting one of said plates diagonallyperpendicular to the direction of said expansion to form twosubstantially equal portions, cutting the other of said platesdiagonally parallel to the direction of said expansion to form twosubstantially equal portions, and connecting edge faces of said fourportions together to form a substantially square composite plate withthe direction of expansion for each of the four portions of a givenelectrical field substantially parallel.

3. In the process of fabricating P-type expander plates, the steps of:providing a substantially square plate of Z-cut P-type crystallinematerial, determining the direction of expansion for said `plate `for agiven exciting electrical field, cutting said plate diagonally into twosubstantially similar portions having triangularly shaped major faceareas, cutting one of said two portions to form two similar portionshaving triangularly shaped major face areas, and connecting edges ofsaid three trangularly shaped portions together with the direction ofexpe nsion for each of the three portions for a given electrical iieldsubstantially parallel to form a rectangularly shaped composite expanderplate.

ci. The process as set forth in claim 3, further characterized in this:that the said diagonal cut is in a direction parallel to the directionof expansion of said plate for the given exciting electrical leld.

5. The process as set forth in claim 3, further characterized in this:that the said diagonal eut is in a direction perpendicular to thedirection of expansion of said plate for the given exciting electricalfield.

6. In the process of fabricating P-type expander plates, the steps of:providing substantially square Z-cut plate means of P-type crystallinematerial, polarizing said plate means to determine the direction ofexpansion for a given exciting electrical field, cutting said platemeans into a plurality of triangular sections, and connecting edge facesof said plurality of triangular sections together to form a compositerectangular expander plate, the directions of expansion of the severaltriangular sections being parallel to' each other and parallel to anedge of said rectangular composite plate.

7. The process as set forth in claim 8, further characterized in this:that said plate means comprises only a single Z-cut plate. and it is eutinto three triangular sections, and edge faces of said three'triangularsections are connected together to form said rectangular compositeplate.

8. The process as set forth in claim 6, further characterized in this:that said plate means comprises a pair of Z-cut plates and each of saidpair of plates is cut into two triangular sections, and edge faces ofsaid four triangular sections are connected together to form saidrectangular composite plate.

9. In the process of fabricating a multi-plate flexing P-typc'piezoelectric unit, the steps of: providing two substantially squareZ-cut plates of P-type crystalline material, polarizing the first ofsaid two plates to determine its direction of expansion for a givenexciting electrical field, cutting said first plate into at least threetriangular sections, connecting edge faces of said plurality oftriangular sections together to form a first composite rectangularexpander plate having the direction of expansion of each of the severaltriangular sections lying parallel to a major edge of said rectangularcomposite plate, polarizing the second of said two plates to determineits direction of expansion for a given exciting electrical field,cutting said second plate into a plurality of triangular sections,connecting edge yfaces of said plurality of triangular sections togetherto form a second composite rectangular expander plate having thedirection of expansion of each of the several triangular sections lyingparallel to a maior edge of said rectangular composite plate. connectingsaid first and said second composite plates together in face-to-facerelationship with their respective directions f expansion for a givenexciting electrical field opposite to each other, and with theconnection lines of one composite plate at substantially right angles tothe connection lines of the other composite plate.

10. As an article of manufacture a piezoelectric crystal unit of themulti-plate flexing type comprising, a first rectangular plate ofpiezoelectric crystalline material adapted to expand along its lengthdimension under the influence of a given electrical field and comprisedof a plurality of triangularly shaped portions connected together attheir edges with the connection lines extending in directions `at 45degrees to the directions of the major edges of said rst rectangularplate, and a second rectangular plate of piezoelectric crystallinematerial adapted to contract along its length dimension under theinfluence of the given electrical field and comprisedl of a plurality oftriangularly shaped portions .connected together at their edges '.viththe connection lines extending 'in directions at 45 degrees tothedirection of the major edges cf said second rectangular plate, saidiii-st and second rectangular plates having substantially the samelength and width dimensions and being connected together in face-to-facerelationship with the said connection lines of one plate extending atsubstantially a 90-degree angle to the said connection lines oi theother plate.

l1. As an article of manufacture a piezoelectric crystal unit of thetype which expands and/or contracts in a. direction substantiallyparallel to the direction of one of its major dimensions comprising, aplurality oi' triangularly shaped plate-like fragments of piezoelectriccrystalline material connected together by their edge faces. saidplurality of triangularly shaped portions being so oriented that theirdirection of expansion for a given exciting electrical field aremutually parallel.

12. As an article of manufacture, a composite plate-like crystal unit ofthe type which expands and/or contracts in a direction substantiallyparallel to the direction of one of its major dimensions, comprising, aplurality of plate-like fragments of piezoelectric crystalline material.cement means connecting said fragments together at their edge faces witheach of said -plurality of fragments so oriented with respect to thecrystallographic axes of the crystalline material that at least one ofits directions of expansion under the influence of a given excitingelectrical field is parallel to the direction of expansion of each ofthe other fragments under the influence of the said given electricalfield, each of the said connected edge faces lying at an angle ofsubstantially 45 degrees to the direction of expansion of said unit.

13. The invention as set forth in claim 12, further characterized inthis: that said article of manufacture comprises a square plate adaptedto expand and/or contract in a direction parallel to its diagonals andfour right angle equilateral triangularly shaped plates, the length ofthe hypotenuse side of each of said triangularly shaped plates beingsubstantially equal to the length of one of the sides of said squareplate, said hypotenuse faces of said four triangularly shaped platesbeing connected to the edge faces of said square plate.

14. As an article of manufacture. a rectangular composite plate-likepiezoelectric unit of the type which expands and/or contracts in adirection substantially parallel to the direction of its majordimension, comprising, three right angle equilateral triangularly shapedplates of piezoelectric material, the length of the hypotenuse side oftwo of said three plates being equal to the length of the leg side ofthe other plate, and cement means connecting said three plates togetherat their edge faces to form a rectangularly shaped composite plate andsaid three triangularly shaped plates being so oriented that a directionof expansion and/or contraction is parallel to the major dimension ofsaid composite rectangular plate.

l5. As an article of manufacture, a composite piezoelectric unitcomprising, four similar right angle equilateral triangularly shapedrplates of piezoelectric material, and cement means connecting said fourplates together at their edge faces lwith said plates oriented to form asquare composite expander plate.

GEZA J. BOKENY.

REFEBEN CES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,766,043 Nicolson June 24, 19301,802,782 Sawyer Apr. 28, 1931 2,105,010 Sawyer Jan. 11, 1938 2,242,756Pope May 20, 1941

